Performance fix - unnecessary rune convertion on --ansi

    > time cat /tmp/list | fzf-0.10.1-darwin_amd64 --ansi -fqwerty > /dev/null

    real    0m4.364s
    user    0m8.231s
    sys     0m0.820s

    > time cat /tmp/list | fzf --ansi -fqwerty > /dev/null

    real    0m4.624s
    user    0m5.755s
    sys     0m0.732s

6 files changed, 52 insertions, 42 deletions

diff --git a/src/chunklist.go b/src/chunklist.go
index c20ffd43..a953fae9 100644
--- a/src/chunklist.go
+++ b/src/chunklist.go
@@ -7,7 +7,7 @@ type Chunk []*Item // >>> []Item
 
 // ItemBuilder is a closure type that builds Item object from a pointer to a
 // string and an integer
-type ItemBuilder func([]rune, int) *Item
+type ItemBuilder func([]byte, int) *Item
 
 // ChunkList is a list of Chunks
 type ChunkList struct {
@@ -26,7 +26,7 @@ func NewChunkList(trans ItemBuilder) *ChunkList {
 		trans:  trans}
 }
 
-func (c *Chunk) push(trans ItemBuilder, data []rune, index int) bool {
+func (c *Chunk) push(trans ItemBuilder, data []byte, index int) bool {
 	item := trans(data, index)
 	if item != nil {
 		*c = append(*c, item)
@@ -53,7 +53,7 @@ func CountItems(cs []*Chunk) int {
 }
 
 // Push adds the item to the list
-func (cl *ChunkList) Push(data []rune) bool {
+func (cl *ChunkList) Push(data []byte) bool {
 	cl.mutex.Lock()
 	defer cl.mutex.Unlock()
 
diff --git a/src/chunklist_test.go b/src/chunklist_test.go
index faaf04fe..26795ef2 100644
--- a/src/chunklist_test.go
+++ b/src/chunklist_test.go
@@ -6,8 +6,8 @@ import (
 )
 
 func TestChunkList(t *testing.T) {
-	cl := NewChunkList(func(s []rune, i int) *Item {
-		return &Item{text: s, rank: Rank{0, 0, uint32(i * 2)}}
+	cl := NewChunkList(func(s []byte, i int) *Item {
+		return &Item{text: []rune(string(s)), rank: Rank{0, 0, uint32(i * 2)}}
 	})
 
 	// Snapshot
@@ -17,8 +17,8 @@ func TestChunkList(t *testing.T) {
 	}
 
 	// Add some data
-	cl.Push([]rune("hello"))
-	cl.Push([]rune("world"))
+	cl.Push([]byte("hello"))
+	cl.Push([]byte("world"))
 
 	// Previously created snapshot should remain the same
 	if len(snapshot) > 0 {
@@ -46,7 +46,7 @@ func TestChunkList(t *testing.T) {
 
 	// Add more data
 	for i := 0; i < chunkSize*2; i++ {
-		cl.Push([]rune(fmt.Sprintf("item %d", i)))
+		cl.Push([]byte(fmt.Sprintf("item %d", i)))
 	}
 
 	// Previous snapshot should remain the same
@@ -64,8 +64,8 @@ func TestChunkList(t *testing.T) {
 		t.Error("Unexpected number of items")
 	}
 
-	cl.Push([]rune("hello"))
-	cl.Push([]rune("world"))
+	cl.Push([]byte("hello"))
+	cl.Push([]byte("world"))
 
 	lastChunkCount := len(*snapshot[len(snapshot)-1])
 	if lastChunkCount != 2 {
diff --git a/src/core.go b/src/core.go
index c0596e33..fdd1e061 100644
--- a/src/core.go
+++ b/src/core.go
@@ -63,48 +63,54 @@ func Run(opts *Options) {
 	eventBox := util.NewEventBox()
 
 	// ANSI code processor
-	ansiProcessor := func(runes []rune) ([]rune, []ansiOffset) {
-		// By default, we do nothing
-		return runes, nil
+	ansiProcessor := func(data []byte) ([]rune, []ansiOffset) {
+		return util.BytesToRunes(data), nil
+	}
+	ansiProcessorRunes := func(data []rune) ([]rune, []ansiOffset) {
+		return data, nil
 	}
 	if opts.Ansi {
 		if opts.Theme != nil {
 			var state *ansiState
-			ansiProcessor = func(runes []rune) ([]rune, []ansiOffset) {
-				trimmed, offsets, newState := extractColor(string(runes), state)
+			ansiProcessor = func(data []byte) ([]rune, []ansiOffset) {
+				trimmed, offsets, newState := extractColor(string(data), state)
 				state = newState
 				return []rune(trimmed), offsets
 			}
 		} else {
 			// When color is disabled but ansi option is given,
 			// we simply strip out ANSI codes from the input
-			ansiProcessor = func(runes []rune) ([]rune, []ansiOffset) {
-				trimmed, _, _ := extractColor(string(runes), nil)
+			ansiProcessor = func(data []byte) ([]rune, []ansiOffset) {
+				trimmed, _, _ := extractColor(string(data), nil)
 				return []rune(trimmed), nil
 			}
 		}
+		ansiProcessorRunes = func(data []rune) ([]rune, []ansiOffset) {
+			return ansiProcessor([]byte(string(data)))
+		}
 	}
 
 	// Chunk list
 	var chunkList *ChunkList
 	header := make([]string, 0, opts.HeaderLines)
 	if len(opts.WithNth) == 0 {
-		chunkList = NewChunkList(func(data []rune, index int) *Item {
+		chunkList = NewChunkList(func(data []byte, index int) *Item {
 			if len(header) < opts.HeaderLines {
 				header = append(header, string(data))
 				eventBox.Set(EvtHeader, header)
 				return nil
 			}
-			data, colors := ansiProcessor(data)
+			runes, colors := ansiProcessor(data)
 			return &Item{
-				text:   data,
+				text:   runes,
 				index:  uint32(index),
 				colors: colors,
 				rank:   Rank{0, 0, uint32(index)}}
 		})
 	} else {
-		chunkList = NewChunkList(func(data []rune, index int) *Item {
-			tokens := Tokenize(data, opts.Delimiter)
+		chunkList = NewChunkList(func(data []byte, index int) *Item {
+			runes := util.BytesToRunes(data)
+			tokens := Tokenize(runes, opts.Delimiter)
 			trans := Transform(tokens, opts.WithNth)
 			if len(header) < opts.HeaderLines {
 				header = append(header, string(joinTokens(trans)))
@@ -113,12 +119,12 @@ func Run(opts *Options) {
 			}
 			item := Item{
 				text:     joinTokens(trans),
-				origText: &data,
+				origText: &runes,
 				index:    uint32(index),
 				colors:   nil,
 				rank:     Rank{0, 0, uint32(index)}}
 
-			trimmed, colors := ansiProcessor(item.text)
+			trimmed, colors := ansiProcessorRunes(item.text)
 			item.text = trimmed
 			item.colors = colors
 			return &item
@@ -128,7 +134,7 @@ func Run(opts *Options) {
 	// Reader
 	streamingFilter := opts.Filter != nil && !sort && !opts.Tac && !opts.Sync
 	if !streamingFilter {
-		reader := Reader{func(data []rune) bool {
+		reader := Reader{func(data []byte) bool {
 			return chunkList.Push(data)
 		}, eventBox, opts.ReadZero}
 		go reader.ReadSource()
@@ -151,7 +157,7 @@ func Run(opts *Options) {
 
 		if streamingFilter {
 			reader := Reader{
-				func(runes []rune) bool {
+				func(runes []byte) bool {
 					item := chunkList.trans(runes, 0)
 					if item != nil && pattern.MatchItem(item) {
 						fmt.Println(string(item.text))
diff --git a/src/reader.go b/src/reader.go
index d979eb6a..3e2cf0a0 100644
--- a/src/reader.go
+++ b/src/reader.go
@@ -5,14 +5,13 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"unicode/utf8"
 
 	"github.com/junegunn/fzf/src/util"
 )
 
 // Reader reads from command or standard input
 type Reader struct {
-	pusher   func([]rune) bool
+	pusher   func([]byte) bool
 	eventBox *util.EventBox
 	delimNil bool
 }
@@ -42,21 +41,10 @@ func (r *Reader) feed(src io.Reader) {
 		// end in delim.
 		bytea, err := reader.ReadBytes(delim)
 		if len(bytea) > 0 {
-			runes := make([]rune, 0, len(bytea))
-			for i := 0; i < len(bytea); {
-				if bytea[i] < utf8.RuneSelf {
-					runes = append(runes, rune(bytea[i]))
-					i++
-				} else {
-					r, sz := utf8.DecodeRune(bytea[i:])
-					i += sz
-					runes = append(runes, r)
-				}
-			}
 			if err == nil {
-				runes = runes[:len(runes)-1]
+				bytea = bytea[:len(bytea)-1]
 			}
-			if r.pusher(runes) {
+			if r.pusher(bytea) {
 				r.eventBox.Set(EvtReadNew, nil)
 			}
 		}
diff --git a/src/reader_test.go b/src/reader_test.go
index bb68e510..d5c218cb 100644
--- a/src/reader_test.go
+++ b/src/reader_test.go
@@ -10,7 +10,7 @@ func TestReadFromCommand(t *testing.T) {
 	strs := []string{}
 	eb := util.NewEventBox()
 	reader := Reader{
-		pusher:   func(s []rune) bool { strs = append(strs, string(s)); return true },
+		pusher:   func(s []byte) bool { strs = append(strs, string(s)); return true },
 		eventBox: eb}
 
 	// Check EventBox
diff --git a/src/util/util.go b/src/util/util.go
index a0e12696..eeeb75f4 100644
--- a/src/util/util.go
+++ b/src/util/util.go
@@ -6,6 +6,7 @@ import "C"
 import (
 	"os"
 	"time"
+	"unicode/utf8"
 )
 
 // Max returns the largest integer
@@ -88,3 +89,18 @@ func TrimRight(runes []rune) []rune {
 	}
 	return runes[0 : i+1]
 }
+
+func BytesToRunes(bytea []byte) []rune {
+	runes := make([]rune, 0, len(bytea))
+	for i := 0; i < len(bytea); {
+		if bytea[i] < utf8.RuneSelf {
+			runes = append(runes, rune(bytea[i]))
+			i++
+		} else {
+			r, sz := utf8.DecodeRune(bytea[i:])
+			i += sz
+			runes = append(runes, r)
+		}
+	}
+	return runes
+}